How can you revoke a vendor’s ACH access to your checking account?

You can do one of two things:

• Put a stop payment claim with your bank (for one-time payments)
• Request your bank to revoke the authorization of payments (you would have to follow this up with the company that is trying to deduct payments as well - else you would/could get hit by other charges).

I believe NACHA rules allows you to revoke authorization, you would need to consult with your bank as to how to best do it.

You can also better understand the ACH rules by visiting http://www.achrulesonline.org/ (Sign-up for the free account).